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WHEN Australian silversmith Ian Ferguson first tried his hand at an old
Japanese metal-working craft, he realised that it wasn’t going to be easy. Try
as he might to forge a neatly layered block of silver and copper, all too often
he ended up with a puddle of molten metal trickling off the anvil.
Overenthusiastic hammer blows sent metal sheets flying in all directions. And in
one unfortunate experiment, when he flattened a block of white-hot metal, a fine
spray of molten brass peppered holes through his clothes. “It felt like being
flayed with a bunch of nettles,” he says.

Not one to give up easily, Ferguson closed his business, sold his house, and
set off for England. With the help of state-of-the-art technology used for metal
bonding research at Oxford University, he has since transformed an arcane craft
into a trusted technique. Now he has started to make masterpieces of fine metal
that would have been beyond the dreams of the original Japanese artists.

The metal-working technique has its roots in ancient Japanese techniques for
decorating the swords of the samurai. Some one hundred years ago, artists began
to diversify, decorating a range of artefacts from opium pipes to vases. Ancient
craftworkers fused layers of different metals together —typically alloys
of copper, silver and gold—then carved and hammered them to expose the
different layers and create multicoloured patterns. The swirling patterns often
looked like knotted wood, giving the technique its name, mokumegane: literally,
“eye of the wood grain metal”.

To achieve this effect, the handful of traditional craftsworkers who still
use the technique stack thin sheets of metal in layers, tie them together with
metal wire, and heat the sheets in a blacksmith’s furnace. Although the
temperatures reached are below the melting point of each metal, the heat excites
metal atoms and encourages them to diffuse into neighbouring layers. The metal
atoms mingle across a region only a few micrometres thick and the divide looks
razor-sharp, but the resulting bond is extremely strong—strong enough that
the melded material can be pressed into a flat sheet without the components
separating.

It’s this flattening part of the process that gives mokumegane its
characteristic fine swirls and lines. Channels, holes or more intricate patterns
are drilled into the layered block before it is flattened. And as the metals
squeeze like toothpaste out of the layers around holes and channels, they rise
to the surface where they appear as stripes, knots and bullseyes.

Ferguson came across the technique at a workshop in Perth, Australia, in
1986. When he went home to try it out, he had little success. Finding the right
moment to remove the metals from the forge seemed impossible. A moment too early
and the sheets simply slid off each other, a moment too late and they melted
into a blob. “You can be a second out and it’s a disaster,” he says.

Eventually, he got the hang of it, but the process was still laborious. As
the metals sat in the forge, he had to watch them like a hawk. This was the only
way to spot the slight darkening of the metals as they drew in energy at the
moment they started to flow. Worse still, the rules had to be completely
rewritten with every new combination of metals.

Colourful combinations

Japanese tradition had restricted the Oriental craft to alloys of silver,
gold and copper, which gave knotted patterns in a limited range of white, grey,
red, brown and black. But using different combinations of metals, Ferguson
reckoned that it should be possible to get shades of yellow, green or even the
oily purple of titanium.

That was easier said than done. For instance, Ferguson wanted to fuse nickel
silver, which contains copper, zinc and nickel and another alloy, called Monel,
which is mainly nickel and copper. This would allow him to create swirls of
black and silver—a colour combination that is impossible using traditional
alloys. But these metals are both extremely stable, and melt at temperatures
above 1100 °C. Encouraging the two to bond proved so difficult that in the
end Ferguson resorted to brute force. He heated the layers until they were white
hot, then dropped a 90 kilogram weight on them from a height of almost 4
metres.

“That got me thinking that there must be a better way,” says Ferguson, who
started to read about modern bonding techniques. He came across diffusion
bonding, which is widely used to make the components of nuclear reactors and
aircraft engines—for instance, to weld the titanium alloy components that
make the fan blades in Rolls Royce aircraft engines. It needs careful control
not only of temperature but also of the pressure used to squeeze the metal
sheets and of the timing of the process. Unfortunately, Ferguson had no access
to the technology for diffusion bonding in Australia. So it was that year, 1991,
that he decided to up sticks and start a PhD at the Royal College of Art in
London.

At the nearby Imperial College of Science, Technology and Medicine, the doors
of the materials science department were opened to him. Ferguson set up a
makeshift diffusion-bonding apparatus—a jig to hold the sheets and a
compression ram that could be placed inside a modern furnace. And with two
stainless steel teapots from a local shop, he built a chamber that he could fill
with the inert gas argon. This stopped some of the reactive metals oxidising and
tarnishing in the heat. Later, he enlarged the gas chamber with more help from
the kitchen suppliers—this time with two asparagus steamers.

Bonding with confidence

For the first time, Ferguson had fairly good control over the process.
Earlier research on diffusion bonding guided his choice of temperature to
between a half and three-quarters of the melting point of the most easily melted
metal. After two years Ferguson had worked up a repertoire of some thirty
combinations that he could bond with confidence. Yet many
combinations—especially using very reactive metals—refused to yield
to his efforts. Then in 1993, the materials science department at Oxford
University offered him access to its state-of-the-art equipment. The diffusion
bonder there can fuse layered cubes up to 5 centimetres on a side under tightly
controlled conditions in a vacuum. These blocks roll out into large sheets about
20 by 30 centimetres.

With a grant from the Leverhulme Trust, which funds interdisciplinary
projects, Ferguson started work with Brian Derby, a metallurgist at Oxford.
Derby, who has researched diffusion bonding for several years, was glad of the
chance to work with the art world. “People have always thought of metals as
being a fairly low-tech, smokestack industry,” he says. “This was an opportunity
to show that you can do pretty things with metals.”

Their aim was to try out some of the more unusual combinations of metals, and
pinpoint the best conditions for bonding them. Derby was able to shed some light
on some of Ferguson’s less successful attempts. For instance, although Ferguson
had succeeded in fusing small blocks of copper and Monel at 900 °C, when he
tried it with larger blocks, the sheets just fell apart. “It was horrible,” says
Ferguson, who examined the debris under an electron microscope. “It came out all
bubbly and flaky.”

Derby diagnosed Kirkendall porosity, which is caused by differences in the
rates at which two metals diffuse into one another. Copper atoms were migrating
to empty sites in Monel’s crystal lattice very efficiently, but nickel atoms
from the Monel were more sluggish about moving to the copper side. Because of
this, the copper became weak and full of holes. Ferguson’s research showed that
he could solve the problem by lowering the temperature to about 600 °C and
increasing the pressure on the block.

The next challenge was to tackle reactive metals such as titanium. When
titanium reacts with oxygen, it becomes coated in an ultrathin transparent film.
Light reflected from above and beneath the oxide film interferes to give a
spectacular rainbow of colours, just like on a film of oil on still water.

But reactive metals also bring problems. Instead of obligingly diffusing into
another metal, titanium reacts with it and binds into a complicated
“intermetallic” compound full of large, elaborate crystals. Metals like copper
deform fairly easily because they have relatively simple crystal structures. But
the large and complex intermetallic crystals are intrinsically brittle. Derby
suspected that rolling layers with intermetallics sandwiched between would make
the material fall apart.

Sure enough, an intermetallic compound showed up under the microscope when
titanium bonded to copper. And as soon as Ferguson started to flatten the
layers, they snapped and cracked into little islands. But to Derby’s surprise,
the material did not crumble. As the islands formed, the much more pliable
copper flowed into the cracks, holding the sheets together. Ferguson then
oxidised the titanium to give islands of irridescent purples, browns and
electric blues in a sea of copper red. “You get these wonderful patterns,” he
says.

Ferguson says that for forty or so metal combinations, he now has a
dependable recipe. “I can guarantee that it will work every time,” he says. He
has already put some of the new metal combinations to use in plates, watch
cases, a decorative egg and several bowls. He has also crafted bowls of copper
and iron, and copper and stainless steel for the Victoria and Albert Museum in
London. Philippa Glanville of the V&A, which is commissioning another bowl
to go on display in November, says Ferguson’s work is the best example of
mokumegane she has seen. “No one has ever applied the process as successfully as
he has,” she says. “The colour combinations are wonderful.”

Ferguson’s work with his new materials has also hinted at all kinds of
curious properties yet to be explored. “I made a bowl out of copper and
stainless steel, and it behaves very strangely,” says Ferguson. “It seems to
have a memory.” After beating it into a bowl he found that the metal tended to
return to its original shape as soon as it was heated.

Ferguson is aware that few people working in mokumegane approve of liaisons
with the world of high-tech. But he insists that you have to have science to be
a good artist. “If you use bad paint and it falls off the canvas, you might
shrug your shoulders and walk away,” he says. “But if your intention was for it
to last a long time, then you’ve failed.”

With help from science, Ferguson and Glanville hope that mokumegane could
flourish in the craft world once again. Ferguson has designed a studio forge
that will allow others to have a go at the craft—but without the sweat and
tears. “I’m hoping more people will take it up,” he says. “I’ve got so many
projects in mind that I haven’t enough time in my life to do them.”